An output switching circuit has been known in which the output voltage is controlled by a switching operation of a transistor.
An output switching circuit has, for example, a PWM generator that performs pulse width modulation (PWM) of an input analog signal and generates a PWM signal and a switching circuit that controls the output voltage by a switching operation based on the PWM signal.
The PWM generator has a triangular wave generating circuit and a comparator, and the voltage of the input analog signal is compared by the comparator with the voltage of the triangular wave generated by the triangular wave generating circuit. A PWM signal at a high level (H level) or low level (L level) is generated when the voltage of the input analog signal is higher or lower than the triangular wave. A D-class amplifier having such an output switching circuit discusses, for example, in Japanese Laid-open Patent Publication No. 2007-67554.
Following the advance in digitalization of electric devices, a demand has grown for scale reduction of analog circuits in output switching circuits. In particular, it is desirable that the scale of analog circuits be reduced in order to combine analog circuits and digital circuits in one chip.
Further, a triangular wave generating circuit installed in the output switching circuit is usually a self-oscillating analog oscillation circuit. For this reason, a spread in oscillation frequency between the triangular wave generating circuits caused by the production spread is difficult to inhibit. As a result, a high yield is not expected in mass production of output switching circuits.